Devices of the kind described above are known from different patent publications, one good example being U.S. Pat. No. 3,987,689, where the two shafts are the output shafts of a vehicle differential mechanism. The device-may accordingly in this case be called a differential brake. There may, however, be other instances when it is desired to counteract a certain rotational speed differential between two shafts, a typical example being the two shafts to the driven front and rear axle, respectively, of a four-wheel-drive vehicle.
Whereas the above-mentioned patent publication shows a "speed-sensitive differential mechanism" and the present invention is applied to the more general case with two axially aligned shafts, the same general considerations apply.
Although U.S. Pat. No. 3,987,689 may be seen as the closest known prior art, there are other publications suggesting neighbouring solutions to the problem of decreasing undesired rotational speed differential between two shafts, such as EP-A-0 350 044, EP-B-0 368 893, U.S. Pat. No. 4 012 968, U.S. Pat. No. 3,488,980 and U.S. Pat. No. 5,087,228.
In a copending patent application from the applicant (SE 9201564-3) two embodiments of a device as defined above are shown. In that case the invention is directed to a controllable restriction in the hydraulic connection from the clutch piston back to the low-pressure side of the pump arrangement for obtaining full control over different parameters or characteristics in a device of this kind.
However, both these embodiments are relatively complex in the design of the hydraulic pump arrangement and its operation.